iPod to iTunes / brand new iMac

hello everyone ....need to know something relatively simple: just set up my brand new iMac (previous PC user), want to get "everything" from my iPod into my new iTunes, saved all iTunes data form PC onto external hard drive, and all of that is in folder on my iTunes desktop now .....when I launched iTunes on my new iMac, it & iCloud only retrieved 19.5 gig of the 37.7 gig of data on my iPod, so now I have to use one of the "iPod to iTunes" utilities like Senuti, etc ....my question: if I use Senuti, etc, will it create doubles of all the songs already in iTunes ?? or will I have to fully delete iTunes before I utilize Senuti, etc ?? I just do not want to see thousands of two of the same song in my iTunes when I finally have everything that is in my iPod in my new iMac's iTunes .....all assists greatly appreciated everyone, thanks much -

via iLounge Forums http://forums.ilounge.com/ipod-classic-legacy-ipods/279788-ipod-itunes-brand-new-imac.html